ACPI: question about functional but not present PnP serial device

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hi

if the status of one serial device is not present
but functional, it's driver is not be loaded on boot, and the device are not be startup , yes or no？

and my question is when is the status of device
not present but functional.

After adding a serial device(e.g. ttyS0) on the
/etc/inittab, when booting the kernel, is the status of the device not present but functional?